The invention relates to “active implantable medical devices” as defined by Directive 90/385/EEC of 20 Jun. 1990 of the Council of the European Communities, specifically implants for stimulation of an elongated cylindrical organ and/or the collection of electrical potentials on such an organ. The invention relates more particularly to the stimulation of nerves, especially the vagus nerve stimulation, in the case of VNS (Vagus Nerve Stimulation) therapy. However, this application is in no way limiting, the invention being possibly used for stimulation/detection of any other organ, or for other purposes such as local delivery of an active agent, etc. to this organ, when the target organ has an elongated cylindrical shape.
The nervous system stimulation therapy is recognized in respect of many disorders such as epilepsy, pain, heart failure, sleep apnea, obesity, etc. The devices used for this purpose include a lead provided with an electrode implanted on the vagus nerve and a generator delivering electrical pulses to this electrode.
VNS therapy typically involves the generation of repetitive pulse bursts, synchronized or not on heart rate depending on the condition to be addressed, these pulses being superimposed on the signals naturally conveyed by the nervous system, and possibly organized in a closed loop. The vagus nerve stimulation may act in efference, directly into an organ, or in afference, to the brain to affect the central nervous system. The waveform of VNS pulses is intended to be interpreted by the central nervous system as a solicitation to produce the expected effects, by prompting the central nervous system to attempt to compensate in opposition to the generated signals.
The invention more particularly relates to a device implanted at the electrode/nerve interface, thereby maintaining the electrode in contact with the nerve or adjacent thereof. Given the approximately cylindrical elongated configuration of a peripheral nerve such as the vagus nerve, the most commonly used device is in the form of a tubular cuff wrapped around the nerve. The cuff is generally made of an elastomer such as silicone, because of the excellent biocompatibility of this material, and it carries on its inner face, applied against the nerve, the stimulation (and/or detection) electrodes.
Such a cuff is, for example, disclosed in U.S. Pat. No. 4,602,624. The cuff described in this document is made from two elastomeric sheets laminated together, one of which being stretched in advance in a preferred pre-stress direction. The resulting composite cuff is then cut to give a rectangular part which, due to the pre-stressing of the one of the sheets, will naturally tend, in the free state, to be wound in a spiral on itself around an axis perpendicular to the biasing direction (a “spiral” being a plane curve being wound regularly around a point from which it deviates more and more).
Compared to a rigid cuff, the cuff described herein has the advantage of simplicity of implementation. The surgeon has just to place it, pass it under the nerve then release it so that it comes from itself to be wrapped around the nerve. Moreover, the cuff is self-adaptive. Indeed, immediately after implantation a normal inflammatory process produces a temporary swelling of the nerve, which then disappears. If one chooses a flexible spiral cuff with an inside diameter slightly smaller than the diameter of the nerve rest, the cuff—with electrodes—always remain closely pressed against the nerve even if the diameter of the latter varies, and without risk of excessive compression that may irreversibly deteriorate nervous tissue.
This device is nevertheless not devoid of drawbacks. A first drawback is present at the time of implantation. To implant the cuff after reaching the target nerve, the surgeon pulls the nerve out of the incision that he created, to slide the unrolled cuff at the selected location. During this maneuver, the tension on the nerve can lead locally to the ends of the sleeve, to relatively high stresses on nerve tissue that can damage them. Another possible cause of the nerve damage is the duration of the procedure, which may expose the nerve to air for too long. It is therefore necessary that the cuff implantation procedure is very short, limiting as much as possible the manipulation of the nerve. Also during implantation, the corners of cuff tend to wind on themselves and impede implantation, which complicates the task of the surgeon.
A second drawback, which appears after implantation, is due to the fact that the innermost edge of the cuff, that is to say, the rolled edge around the nerve bears against the latter and exerts along the contact line pressure which tends to force or even distort the nerve. The risk also exists that during implantation the surgeon allowed the outer edge of the cuff to roll in the opposite direction, which then forms a second turn in the opposite direction to the first. The radius of curvature is no longer the one that was expected, with consequently potential complications.
Finally, a third drawback is linked to the manufacturing process. As mentioned above, the cuff is made by laminating together two elastomeric sheets, with a directional pre-stress applied to one of them. These sheets being very thin (their typical thickness is about 100 μm), problems of homogeneity of the material and of thickness tolerance can appear in the extent of the surface of a same sheet as well as between two sheets, limiting the reproducibility of the production process of the cuffs. It is certainly possible to overcome this disadvantage by using large sheets, but with a negative impact on the industrial process. It is also possible to use thicker sheets, more easily controllable during the process, but with an increased damage risk of the nerve due to less flexibility and therefore the lesser ability of the cuff to conform to the morphology of the nerve in the implantation zone.
Another type of cuff is disclosed in DE 10 2007 036 862 A1, which discloses a strip-shaped elongate element of flexible material (silicone) carrying one or two electrodes formed in a central region. This strip is further provided on one side of the central region, of a hole or of a transverse slot, and the opposite side has a tapered shape which, after winding around the nerve, may be introduced into the slot so as to grip the cuff on the nerve, like a cable tie imprisoning an electrical wire harness.
Compared to the first type of cuff described above, this second type has multiple drawbacks:                It is not a “self-rolling” cuff, in that it is not sufficient to unwind and to release it for it comes by itself in position as a spiral around the nerve. It rather requires a manipulation of the surgeon to introduce the tapered end into the slot and secure the cuff around the nerve;        It leaves two long projections extending radially from the implantation site (the portion bearing the slot, and by the portion tapered after insertion into the slot);        The position of the electrodes in a central region of the ribbon complicates the accurate placement of these electrodes at the selected stimulation site;        It is not “self-adapting.” The degree of tightening varies with the diameter of the nerve, which may change, for example under the effect of a temporary swelling reaction after implantation; and        The degree of tightening the cuff on the nerve is totally operator-dependent since the tightening depends on the length of the protruding portion of the slot—hence a possible insufficient tightening (leading to incorrect application of electrodes against the nerve) or, conversely, excessive tightening (with the risk of irreversible damage to nerve tissue).        
The need therefore exists for a self-rollable thin elastomeric cuff which can be produced by an effective industrial method, with a high degree of reproducibility, without the use of thick sheets that lead to products that are not fully satisfactory in terms of use.